Air-conditioning system for a motor vehicle

ABSTRACT

In an air-conditioning system for motor vehicles, the radiator for heating the passenger compartment is excluded from connection to the circuit for cooling the engine when heating of the passenger compartment is not required. In this condition, a mixing valve is set in an intermediate position, in which part of the flow of air leaving the evaporator of the system flows directly in the passenger compartment of the motor vehicle, keeping it cooled, while part of the flow of air leaving the evaporator flows through the aforesaid heating radiator, which in this condition functions as accumulator of cold. When the cooling circuit is temporarily deactivated, cooling of the passenger compartment can be ensured by the radiator, that yields the previously accumulated cold.

FIELD OF THE INVENTION

The present invention relates to air-conditioning systems for motorvehicles, of the type comprising:

an evaporator for cooling the air, forming part of a cooling circuit andinterposed in a path of a flow of air;

a radiator for heating air, connected to the circuit of the liquid forcooling the internal-combustion engine of the motor vehicle, and set inthe aforesaid path of the flow of air, downstream of the evaporator; and

a mixing valve, for example in the form of an oscillating flap, fordirecting the flow of air leaving the evaporator all through the heatingradiator, or else all directly to the passenger compartment withoutpassing through the heating radiator, or else part through the heatingradiator and part directly to the passenger compartment.

In all vehicles with internal-combustion engine, turning-off of theengine entails simultaneous interruption of the generation of cold onaccount of arrest of the compressor forming part of the cooling circuit.Normally in fact, said compressor is driven by the internal-combustionengine (the problem discussed here does not exist in the cases where thecompressor is driven by an electric engine). When the engine of themotor vehicle stops, the evaporator of the cooling circuit loses itscapacity for cooling the flow of air directed to the passengercompartment of the motor vehicle on account of the lack of a flow ofcoolant inside it. In said condition, the evaporator tends to heat up ina few seconds. Said phenomenon penalizes above all motor vehiclesequipped with a stop-and-start system in which, whenever thestop-and-start strategy is implemented causing turning-off of theengine, the cooling circuit ceases to perform its function of cooling ofthe passenger compartment.

To overcome said drawback, it has been proposed to adopt, instead of anevaporator of a conventional type, a special evaporator including aportion that is not designed for generation of cold air to be usedimmediately, but rather for accumulation of cold, for subsequentyielding of the cold accumulated at the moment in which the engine ofthe motor vehicle is turned off. Said solution basically entails anincrease in the thermal inertia of the evaporator such as to slow downheating thereof whenever the cooling circuit ceases to function.However, said solution slows down the initial step of cooling of thepassenger compartment of the motor vehicle when the engine is startedafter a stop in so far as part of the cold generated by the coolingcircuit is not used immediately for cooling the passenger compartment,but is used to cool the part of the evaporator that functions asaccumulator.

Object of the invention

The object of the present invention is to overcome the drawbacks of theknown art by providing an air-conditioning system that will guarantee anefficient cooling of the passenger compartment of the motor vehicle inany condition of operation and in particular also during temporaryarrests of the engine, such as for example following upon activation ofa stop-and-start device.

SUMMARY OF THE INVENTION

A further object of the invention is to achieve the aforesaid targetwithout penalizing the efficiency of cooling in any other condition ofoperation and in particular at starting of the engine after a prolongedstop of the motor vehicle.

Yet a further object of the invention is to achieve the aforesaid targetwith simple and low-cost means.

With a view to achieving the above objects, the subject of the inventionis an air-conditioning system having the characteristics that have beenreferred to at the start of the present description and furthercharacterized in that, in the connection between the heating radiatorand the circuit of the liquid for cooling the engine, a by-pass valve isprovided, which can be activated for excluding the heating radiator fromthe circuit of the liquid for cooling the engine, and in that controlmeans are provided, configured for activating said by-pass valve and forkeeping the aforesaid mixing valve in an intermediate position whenheating of the passenger compartment is not required and the coolingcircuit is active, so that in said conditions the radiant mass of saidheating radiator functions as accumulator of cold, which can besubsequently used for keeping the passenger compartment cooled alsoduring a temporary arrest of the cooling circuit.

In the system according to the invention, when the aforesaid by-passvalve is activated, the radiator for heating air is no longer involvedin the circulation of the liquid for cooling the engine and can henceperform the function of accumulator of cold. Said solution hence enablesseparation of the function of generation of the cold that is to beimmediately used for cooling the passenger compartment of the motorvehicle, which is performed by the evaporator of the cooling circuit,from the function of accumulation of cold to be used subsequently,during temporary arrests of the engine, which is performed by theheating radiator. Consequently, in normal conditions of operation, andin particular after starting of the engine subsequent to a prolongedstop of the vehicle, the entire mass of the evaporator can be dedicatedto cooling the passenger compartment of the motor vehicle immediately soas to reduce to a minimum the time necessary for bringing the passengercompartment to the preferred temperature. At the same time, duringtemporary stoppages of the engine caused, for example, by astop-and-start device, the mass of the heating radiator, previouslycooled in the accumulation step, guarantees the flow of cold air to thepassenger compartment.

A further subject of the present invention is the method for controllingthe air-conditioning system that is implemented by means of the systemdescribed above.

Preferably, the aforesaid control means are electronic control meansdesigned to control both activation of the aforesaid by-pass valve andthe position of the aforesaid mixing valve, as well as operation of thecompressor of the cooling circuit. In said preferred embodiment, theelectronic control means are pre-arranged for activating the function ofaccumulation of cold by the heating radiator also during the steps ofdeceleration of the vehicle.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the invention will emerge fromthe ensuing description with reference to the annexed drawings, whichare provided purely by way of non-limiting example and in which:

FIG. 1 is a scheme of the internal-combustion engine of motor a vehicleand of a radiator for heating the passenger compartment of the motorvehicle connected to the circuit for cooling the engine, implementedwith the by-pass valve provided in the system according to theinvention;

FIGS. 2 and 3 illustrate a scheme of a system for supplying the air tothe passenger compartment of the motor vehicle in two differentoperating conditions, according to the strategy forming the subject ofthe present invention; and

FIGS. 4 and 5 are diagrams illustrating the advantages of the presentinvention with reference to the efficiency of cooling of the passengercompartment of the motor vehicle also in the steps in which thecompressor of the cooling circuit is stopped.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is applied to a motor vehicle equipped with aninternal-combustion engine 1 (illustrated as a whole in FIG. 1) and witha radiator 2 for heating the passenger compartment of the motor vehicleconnected to the circuit for cooling the engine 1. In particular, withreference to FIG. 1, the radiator 2 receives hot liquid leaving thecircuit for cooling the engine 1 via a first connection duct 3. The hotliquid traverses the radiator 2, according to the conventionaltechnique, yielding heat to the radiant mass of the radiator 2 and thenreturns into the circuit for cooling the engine 1 via a duct 4.

For the purposes of the present invention, the conventional arrangementdescribed above is implemented by introducing into the inlet duct 3 ofthe radiator 2 a by-pass valve 5, of any known type, preferablycontrolled electronically by a control unit E. When the by-pass valve 5is inactive, it does not prevent arrival of hot liquid coming from theengine 1, through the duct 3, up to the radiator 2. When the by-passvalve 5 is activated, it causes the hot liquid coming from the engine toflow in a by-pass duct 6 converging in the return duct 4 so that theradiator 2 is not traversed by the circulation of the liquid for coolingthe engine.

FIG. 2 shows in cross section, in a vertical plane parallel to thelongitudinal direction of the motor vehicle, an example of embodiment ofan assembly for supplying conditioned air to the passenger compartmentof a motor vehicle. The assembly 7 has a structure 8, with an outlet 9for the flow of conditioned air, on which the dashboard of the motorvehicle (not illustrated) rests. According to the conventionaltechnique, the dashboard is provided with one or more mouths for outflowof the air both adjacent to the windscreen of the motor vehicle and inthe front part of the dashboard, as well in the proximity of the floorpanel of the motor vehicle, for directing conditioned air within thepassenger compartment 10 (in FIG. 2 the direction of advance of themotor vehicle is indicated by the arrow A).

According to a technique in itself known, the assembly 7 includes a fan11 for supplying a flow of air F to the passenger compartment 10 of themotor vehicle, through the mouths in the dashboard. Set along the pathof the flow F is an evaporator 12 forming part of the cooling circuitwith which the motor vehicle is equipped, with an inlet duct 12 a and anoutlet duct 12 b for the fluid of the cooling circuit.

Also set downstream of the evaporator 12, along the path of the flow ofair F, is the radiator 2 for heating the passenger compartment, with theoutlet ducts 3, 4.

Once again according to a technique in itself known, set between theevaporator 12 and the heating radiator 2 is a mixing valve M, which inthe example illustrated is constituted by a flap mounted oscillatingabout an axis M1 and mobile (preferably by means of an electric enginecontrolled by the electronic control unit E) between a first operatingposition (illustrated in FIG. 2), in which the entire flow of airleaving the evaporator 12 is conveyed directly to the outlet 9 and intothe passenger compartment 10 of the motor vehicle, without being made topass through the radiator 2, and an opposite operating position(illustrated with a dashed line in FIG. 2), in which the entire flow ofair leaving the evaporator 12 is conveyed through the heating radiator 2before being sent to the passenger compartment 10 (as indicated by thearrows G).

As may be seen in FIG. 3, the mixing flap M can be set in anintermediate position, in which the flow of air leaving the evaporator12 splits into two flows: a first flow F1 traverses the radiator 2 andthen reaches the outlet 9, whilst a second flow F2 is sent directly tothe outlet 9 and to the passenger compartment 10 without passing throughthe heating radiator 2.

As has already been discussed above, conventional systems in which thecompressor of the cooling circuit is driven by the internal-combustionengine of the motor vehicle present the drawback of an interruption ofcooling of the passenger compartment during a temporary arrest of theengine due, for example, to activation of a device of the stop-and-starttype. In order to overcome said drawback, according to the presentinvention there is envisaged, as already mentioned, the use of theaforesaid by-pass valve 5, which enables exclusion of the heatingradiator 2 from the circulation of the liquid for cooling the engine,and the control means of the by-pass valve 5 and of the mixing valve Mare configured (in the case illustrated herein by means of softwareprogramming of the electronic control unit E) so that in a condition ofoperation in which the passenger compartment of the motor vehicle doesnot have to be heated and the cooling circuit is active, the valve 5 isactivated for excluding the radiator 2 from the circulation of thecooling liquid, and the mixing valve M is set in an intermediateposition like the one illustrated in FIG. 3 so as to cause in any case apart of the flow of air leaving the evaporator 12 to pass through theradiator 2. In said conditions, part of the flow of cold air is conveyeddirectly to the passenger compartment of the motor vehicle and is thenimmediately used for cooling the passenger compartment, but another partof the flow of cold air leaving the evaporator is made to pass throughthe radiator 2, the radiant mass of which functions as accumulator ofcold.

In this way, if the operation of the cooling circuit is subsequentlyinterrupted temporarily (for example, in so far as the engine of themotor vehicle stops following upon implementation of a strategy of thestop-and-start type) a flow of cold air continues to be supplied to thepassenger compartment 10 owing to the fact that it traverses theradiator 2, which in this step yields the cold previously accumulated.Preferably, in said step of exploitation of the cold accumulated by theradiator 2, the mixing valve M is brought into the position representedby a dashed line in FIG. 2, where the entire flow of air is forced topass through the radiator 2.

As may be seen, the system according to the invention envisages that theradiator for heating the passenger compartment 10 can be used, when saidheating is not necessary, as accumulator of cold during the steps inwhich heating of the passenger compartment is not required and thecircuit for cooling the motor vehicle is active in such a way as to beable to exploit the cold accumulated by said radiator in the steps inwhich cooling of the passenger compartment is desired but the coolingcircuit is inactive.

FIGS. 4 and 5 show the advantages of the invention (FIG. 5) as comparedto the conventional solution (FIG. 4).

In the case of conventional systems, the situation is the oneillustrated in FIG. 4. In said figure, the line T indicates thevariation in time of the temperature of the air entering the passengercompartment of the motor vehicle, starting from an instant zero in whichthe compressor of the cooling circuit is activated. As may be seen, thetemperature, which is initially high, drops progressively following uponcooling of the flow of air through the evaporator 12. In FIG. 4, theline C indicates (in percent) the electrical signal for driving thecompressor of the cooling circuit. As may be seen, said figure shows anexample in which operation of the compressor is temporarily interruptedfor two minutes at the instant t=32 min. Following upon saidinterruption, the temperature of the air undergoes a sharp rise in thesame time interval, and then starts to drop again when the compressor isre-activated.

FIG. 5 shows the same diagrams obtained with the present invention. Asmay be seen, in the step of interruption of operation of the compressorC, the temperature of the air rises only slightly thanks to the factthat, as illustrated, in said step there is in any case exploited thecold accumulated by the radiator 2. In FIG. 5, the diagram D indicatesthe percentage of air that is supplied to the radiator 2 via the mixingvalve M. As may be seen, when the compressor is turned off, the valve Mis set in the position that feeds the entire flow of air through theradiator 2 in such a way as to exploit fully the cold previouslyaccumulated therein.

In the case of application of the invention to an air-conditioningsystem provided with electronic control of the compressor, it ispossible to optimize the step of accumulation of cold by exploiting thesteps of deceleration of the vehicle for increasing the production ofcold that is to be accumulated.

The by-pass valve 5 of the radiator 2 can then be used also during thewinter season for accelerating the step of heating of the engine after acold start, momentarily excluding the heating radiator 2 during saidstep of heating of the engine.

Of course, without prejudice to the principle of the invention, thedetails of construction and the embodiments may vary widely with respectto what has been described and illustrated herein purely by way ofexample, without thereby departing from the scope of the presentinvention.

1. An air-conditioning system of a motor vehicle, comprising: an evaporator for cooling the air, forming part of a cooling circuit, and interposed in a path of a flow of air; a radiator for heating the air, connected to the circuit of the liquid for cooling the engine and set in the aforesaid path of the flow of air, downstream of the evaporator; and a mixing valve for directing the flow of air leaving the evaporator all through the heating radiator, or else all directly to the passenger compartment, without passing through the heating radiator, or else part through the cooling radiator and part directly to the passenger compartment, wherein, in the connection between the heating radiator and the circuit of the liquid for cooling the engine, a by-pass valve is provided that can be activated for excluding the heating radiator from the circuit of the liquid for cooling the engine; and in that control means are provided, configured for activating said by-pass valve and for keeping the aforesaid mixing valve in an intermediate position when heating of the passenger compartment is not required and the cooling circuit is active so that in said conditions the radiant mass of said heating radiator functions as accumulator of cold, which can be subsequently used for keeping the passenger compartment cooled also during a temporary arrest of the cooling circuit.
 2. The system according to claim 1, wherein said control means are electronic control means programmed for keeping said mixing valve in said intermediate position when heating of the passenger compartment is not required and the cooling circuit is active so as to exploit the radiant mass of the heating radiator as accumulator of cold, said electronic control means being instead programmed for displacing the mixing valve into a position in which the entire flow leaving the evaporator is forced to pass through the heating radiator in the conditions in which cooling of the passenger compartment is desired and the cooling circuit is temporarily inactive so as to exploit to the maximum the cold accumulated in the radiator for keeping the passenger compartment cooled.
 3. The system according to claim 1, wherein said control means are electronic control means programmed for activating the step of accumulation of cold in the radiator also in the steps of deceleration of the vehicle.
 4. A method for controlling an air-conditioning system of a motor vehicle, wherein said system comprises: an evaporator for cooling the air, forming part of a cooling circuit, and interposed in a path of a flow of air; a radiator for heating the air, connected to the circuit of the liquid for cooling the engine and set in the aforesaid path of the flow of air, downstream of the evaporator; and a mixing valve for directing the flow of air leaving the evaporator all through the heating radiator, or else all directly to the passenger compartment, without passing through the heating radiator, or else part through the heating radiator and part directly to the passenger compartment, wherein, in the connection between the heating radiator and the circuit of the liquid for cooling the engine, pass valve is provided that can be activated for excluding the heating radiator from the circuit of the liquid for cooling the engine, and in that, when heating of the passenger compartment is not required and the cooling circuit is active, the aforesaid by-pass valve is activated and the aforesaid mixing valve is set in an intermediate position so that in said condition the radiant mass of said heating radiator functions as accumulator of cold, which can subsequently be used for keeping the passenger compartment cooled also during a temporary deactivation of the cooling circuit.
 5. The method according to claim 4, wherein said mixing valve is kept in the aforesaid intermediate position when heating of the passenger compartment is not required and the cooling circuit is active, whilst said mixing valve is set in a position where the entire flow leaving the evaporator is forced to pass through said heating radiator to exploit the cold accumulated therein when cooling of the passenger compartment is required and the cooling circuit is temporarily deactivated.
 6. The method according to claim 4, wherein the step of accumulation of cold in the heating radiator is also activated during the steps of deceleration of the vehicle. 